Bitumen recovery from oil sands is a challenging activity that requires accessing subterranean bitumen, extracting the bitumen from the subterranean sand and then recovering the bitumen from the subterranean location to above ground. There are numerous proposed methods for recovering bitumen from oil sands. The Background section of US Publication US2008/0139418 provides a review of many recovery methods including strip mining, cold flow technique, cyclic steam stimulation (CSS), steam assisted gravity drainage (SAGD) and vapor extraction process (VAPEX).
CSS and SAGD processes are “hot” processes (that is, thermal methods) that use hot steam to decrease the viscosity of subterranean bitumen. In these processes steam is injected down a first well into subterranean oil sands. The steam penetrates the sands and lowers the viscosity of bitumen by heating the oil sands, which facilitates flow of the bitumen through the sands into either the first well (CSS) or to a second well (SAGD) from which recovery of the bitumen occurs. With the CSS method, steam is injected into a well at temperatures of 250° C.-400° C. The well then sits for days or weeks during which time the steam heats bitumen in the subterranean environment around the well causing bitumen to drain into the well and after which hot oil mixed with condensed steam is pumped out from the well for weeks or months. Then the process is repeated. In the SAGD process two horizontal wells are drilled, one below the other (generally approximately five meters apart). Steam is injected into the upper well, heating bitumen in the surrounding subterranean environment thereby lowering the viscosity of the bitumen causing it to flow into the lower well. The resulting bitumen and condensed steam mixture is subsequently pumped to the surface from the bottom well. According to US Publication US 2008/0139418, recovery of bitumen from an oil sands reservoir by CSS is typically only about 20-25 percent (%) while recovery in SAGD processes is reportedly up to about 60% of the available bitumen in the oil sands reservoir.
A modified version of the SAGD process is also known. U.S. Pat. No. 6,230,814 describes what has become known as the expanding solvent steam assisted gravity drainage (ES-SAGD) process. The ES-SAGD process requires combining hydrocarbons with steam in a SAGD-type process so the hydrocarbons can solubilize bitumen in subterranean oil sands to further reduce bitumen viscosity to facilitate the drainage of bitumen into a second well hole for recovery to above ground. The reference identifies suitable additives as hydrocarbons having from one to 25 carbons.
Challenges of thermal methods include low recovery rate (40 to 60 percent of oil in place) and high energy and water usage. One approach to improving well performance (higher oil rate, higher recovery, or lowered steam usage) is by the addition of a chemical agent to the steam injection stream. The potential utility for several different types of chemicals has been demonstrated, including glycol ethers, amines, and surfactants, see U.S. Pat. Nos. 3,396,792 and 3,454,095; US Patent Application No. 2009/0078414 and 2009/0218099; and U.S. Provisional Application Ser. Nos. 61/806,067 and 61/739,279. However, continuous addition of such steam additives is expensive and impractical.
It would be desirable to have a steam enhanced recovery process that improves bitumen and/or heavy oil recovery rate while being economical viable.